Field of the Invention
The present invention relates to an electrode material for a lithium ion secondary battery, an electrode for a lithium ion secondary battery, and a lithium ion secondary battery.
Description of Related Art
Electrode materials made of LiMnPO4 are materials allowing anticipation of a higher battery reaction voltage and an approximately 20% higher energy density (mass energy density) than electrode materials made of LiFePO4. Therefore, electrode materials made of LiMnPO4 are anticipated to be developed for use in electric vehicle-oriented secondary batteries.
However, in a lithium ion secondary battery with a positive electrode including an electrode material made of LiMnPO4, due to the low electron conductivity of LiMnPO4 bulk, the low Li diffusivity of the LiMnPO4 bulk, and the Jahn-Teller effect of manganese ions (Mn2+), the volume of LiMnPO4 crystals significantly changes in an anisotropic manner as a battery reaction proceeds. Therefore, in a lithium ion secondary battery with the above-described constitution, the activation energy for intercalating and deintercalating lithium ions into and from the positive electrode increases. As a result, the battery characteristics of the lithium ion secondary battery at a low temperature significantly degrade.
In order to improve the battery characteristics of the lithium ion secondary battery at a low temperature, active studies are underway regarding LiFexMn1−xPO4 (0<x<1) obtained by substituting some of Mn by Fe in LiMnPO4 (for example, refer to Japanese Unexamined Application, First Publication No. 2013-101883). In LiFexMn1−xPO4, since Fe forms a solid solution, the electron conductivity in particles improves more than in LiMnPO4. As a result, in a lithium ion secondary battery with a positive electrode including an electrode material made of LiFexMn1−xPO4, the charge and discharge performance improves.
However, there has been no report regarding examples in which an electrode material capable of realizing lithium ion secondary batteries having excellent battery characteristics, for example, at a low temperature and at a high-speed charge and discharge are obtained using the method described in Japanese Unexamined Application, First Publication No. 2013-101883.
Studies are underway regarding LiFexMn1−x−yMyPO4 which is obtained by substituting Mn by a bivalent metal in LiFexMn1−xPO4 to obtain a high energy density in the case in which LiFexMn1−xPO4 is used as an electrode material by further improving electrical characteristics of LiFexMn1−xPO4 (for example, refer to Published Japanese Translation No. 2013-518378 of the PCT International Publication and Published Japanese Translation No. 2013-518023 of the PCT International Publication).